In an automotive cooling system, an electronically controlled valve or other flow control device may control the temperature of a coolant at one point in the system, such as at the entry point of the coolant into the propulsion system of a vehicle, for example. The temperature of the coolant at this point in the system, known as the valve temperature, can be measured by a temperature sensor. The valve or other flow control device may control the valve temperature of the coolant at this point, according to a target temperature or valve set point temperature, by varying the ratio of the quantity of coolant flowing through a radiator or other heat exchanger to the quantity of coolant bypassing the radiator or heat exchanger and flowing into the propulsion system of the vehicle.
Under certain operating conditions, there may be situations, which call for additional temperature requirements at another point in the cooling system. These situations could include, for example, situations in which cabin heating and/or windshield defrosting is/are required. One of these additional temperature requirements could be that of the coolant entering a heater core, which provides heated air to the vehicle cabin, for example. At this point in the system, a heater temperature of the coolant would be measured by a different temperature sensor than that used to measure the valve temperature. The heater temperature requirement at that point in the system, corresponding to a heater set point temperature, may be different from the valve temperature requirement. Furthermore, the cooling system may include a coolant heater, which can be operated to augment the heater temperature of the coolant in order to achieve the heater set point temperature requirement at this point in the system.
In heating situations, the coolant heater typically consumes energy in order to heat the coolant. In meeting heater set point temperature requirements, it is therefore desirable to minimize the quantity of energy consumed by the coolant heater in order to maximize vehicular energy efficiency. For various reasons, the valve set point temperature may be lower than the heater set point temperature. The situation can therefore arise in which the heater set point temperature calls for the addition of heat from the coolant heater whereas the valve set point temperature simultaneously calls for the dissipation of heat from the radiator. This can lead to reduced vehicular energy efficiency because the coolant heater is consuming energy to add heat to the coolant while the valve is distributing the coolant through the radiator in order to draw the heat back out of the coolant.
Therefore, a control strategy is needed in which the valve set point temperature changes to more closely match the heater set point temperature when a heating situation arises and reverts to a value, which is optimal for cooling of the propulsion system when a heating situation does not exist. Such a strategy would facilitate optimum energy efficiency throughout all operating conditions.